Preparation of cellulose xanthate from sheeted cellulose fiber



Patented Oct. 31, 1933 PREPARATION OF CELLULOSE XANTHATE FROM SHEETED CELLULOSE FIBER- George A. Richter, Berlin, N. ,l-l assignor to Brown Company, Berlin, N. H., a corporation of Maine No Drawing. Application September 11, 1931 Serial No. 562,432

Claims;

This invention relates to the preparation of cellulose xanthate from sheeted cellulose fiber. In making cellulose xanthate, the current practice involves dipping comparatively thick sheets of substantially unbeaten wood pulp, e. g., drier sheets so-called, in a mercerizing caustic soda solution, i. e., one of about 18% strength, at room or even lower temperatures. There are many pulps which tend to disintegrate from sheet form and to become pulpy masses difiioult to handle when submersed in a caustic soda solution under these conditions to form soda cellulose. For example, sheets of kra'ft or soda pulp or refined pulp prepared from Matt or soda pulp tend to fall apart when subjected to :this first step of the xanthating process. This disintegration is attributable to an undue swelling of the fiber accompanying mercerization and to a dissolving of ingredients like pentosans and 001- loidal celluloses, which ordinarily serve to bond the fibers together and thus to hold the sheets intact. v

I have found that, despite the fact that little mercerization of the fiber ensues at temperatures above about 40 0., it is nevertheless of distinct advantage to carry out the clipping of sheets of fiber in caustic soda solutions of at least about 18% strength at temperatures above about 40 C. Thus, at such elevated temperatures, there is no diiiiculty in maintaining the sheets intact even when they are formed from kraft pulp. Whereas the sheets expand greatly in thickness in solutions of about 18% strength at'room temterature and in so doing tend to fall apart, there is less such action when the solution is maintained at temperatures above about 40 0., say between 40' to 80 C. In addition to the advantage of maintaining the integrity of the sheets, the hot solution promotes a removal from the fiber of resins, gums, and other contaminations which impair the clarity of the viscose solution into which the soda cellulose is converted. The hot solution also promotes a lowering of the solution viscosity of the pulp, wherefore, the soda cellulose needs little, if any, ageing prior to being xanthated and dissolved to form a viscose solution. Again, it becomes feasible to add to the solution small quantities of suitable oxidants, such as hypochlorites and peroxides, which to greatly assist in lowering the solution viscosity of the pulp, since they are quickly consumed at elevated temperature. The use of oxidants is not practical at room or lower temperatures, because one must put up either with a long period of reaction or with the presence of unconsumed a hot solution is of advantage even when applied to pulps generally, that is, to pulps of varione derivations, including sulphite pulp sheets, refined Wood pulp sheets, and cotton linter sheets, all of which have little disintegrating tendency when subjected to the usual step of making soda cellulose.

After the initial high temperature immersion in caustic soda solution, the sheets may be squeezed free from excess solution, whereupon thedesired mercerization of the fiber. may be realized by the simple expedient of cooling the sheets .to room or lower temperatures. The squeezing of the-excess solution at temperatures above 20. C. is easier because caustic soda solutions of 18% strength are much more viscous at 20 C. thanthey are at appreciably higher temperatures. The mercerization, being accomplish'ed Without a large excess of caustic soda solution surrounding the sheets such as prevails in the soaking bath, is not accompaniedby any disintegrating effect on the sheets. The cooling so of the sheets may be accomplished as a separate step in an artificially refrigerated atmosphere, or by mere exposure to room temperature. Or the sheets may be taken directly from the press and shredded or broken up into soda cellulose 35 crumbs, as ordinarily, in a grinder or disintegrator, during which operation, or afterwards, the massof fiufiy soda cellulose may be cooled. The grinderor disintegrator employed may be of the usual type, which is jacketed to permit a refrigerating medium to be circulated through the jacket, so as to chill the soda cellulose crumbs. The crumbs of soda cellulose, after having been cooled to a temperature of about 26 C. or lower, are ready, with or without ageing,

to be converted into cellulose xanthate by treatment with carbon bisulphide. The cellulose xanthate may then be dissolved as customarily in dilute alkali solution to form a viscose solution.

. The principles of the present invention apply most-advantageously to sheets of unbeaten pulp which are susceptible to disintegration in caustic soda solutions of at least about 18% strength at room temperature (18 to 21 C.) or lower. Included in this category of pulps are not only alkali-liberated pulps like kraft and soda, but also those pulps liberated from short-fibered woods exemplified by soft Woods of the type of poplar and by hardwoods in general. The shortfibered pulps are troublesome in sheet form, because there is evidently insufficient interfelting between the fibers to resist separation and individualism of the fibers upon their swelling and curling, such as ensues from submergence in a bath of caustic soda solution'under mercerizing conditions.

There is advantage in carrying out the initial treatment with caustic soda solution of at least about 18% strength at temperatures above about 40 C. even when the cellulose pulp serving as the raw material is other than in sheet form, for instance, in the form of loose bulk pulp. While the treatment is devised primarily to prevent sheet cellulose from disintegrating into pulpy masses, of importance too, is the fact that the treatment is conducive to an improved, low-viscosity soda cellulose which can be xanthated with little ageing.

I claim:

1. In the manufacture of cellulose xanthate, those steps which comprise treating cellulose pulp with excess caustic soda solution of about 18% strength and containing an oxidant at temperatures above about 40 C., removing the excess solution, cooling the soda cellulose so prepared to a temperature at which mercerization is effected, and xanthating the cooled mercerized product.

2. In the manufacture of cellulose xanthate, those steps which comprise maintaining sheets of cellulose pulp immersed at temperatures above about 40 C. in a caustic soda solution of about 18% strength and containing an oxidant until the oxidant is substantially consumed, removing the sheets from the solution, cooling the soda cellulose so prepared to a temperature at which mercerization is eifected, and xanthating the cooled, mercerized product.

3. In the manufacture of cellulose xanthate, those steps which comprise dipping sheets of cellulose pulp, characterized by their tendency to disintegrate in a mercerizing bath at normal temperature, in a bath of caustic soda solution of about 18% strength at temperatures above about 40 C., removing the substantially unmercerized sheets from the solution, cooling the soda cellulose so prepared to a temperature at which mercerization is effected, and xanthating the cooled, mercerized product.

4. In the manufacture of cellulose xanthate, those steps which comprise dipping sheets of alkali-liberated wood pulp in a caustic soda solution of about 18% strength at temperatures above about 40 0., removing the sheets from the solution, cooling the soda cellulose so prepared to a temperature at which mercerization is effected, and xanthating the cooled, mercerized product.

5. In the manufacture of cellulose Xanthate, those steps which comprise dipping sheets of short-fibered wood pulp derived from woods of the nature of poplar and hardwoods in a caustic soda solution of about 18% strength at temperatures above about 40 C., removing the sheets from the solution, cooling the soda cellulose so prepared to a temperature at which mercerization is effected, and xanthating the cooled, mercerized product.

6. In the manufacture of cellulose xanthate, those steps which comprise dipping sheets of wood pulp in a caustic soda solution of about 18% strength at temperatures of about 40 to C., removing the sheets from the solution, cooling the soda cellulose so prepared to a temperature downwards of about 20 C. to efiect mercerization, and xanthating the cooled, mercerized product. 7

7. In the manufacture of cellulose xanthate, those steps which comprise dipping sheets of cellulose pulp in a bath of caustic soda solution of about 18% strength at temperatures above 40 C., removing the substantially unmercerized sheets from the solution, cooling the soda cellulose so prepared to a temperature at which mercerization is effected, and xanthating the cooled, mercerized product.

8. In the manufacture of cellulose xanthate, those steps which comprise dipping sheets of wood pulp in a bath of caustic soda solution of about 18% strength at temperatures above 40 0., removing the substantiallyunmercerized sheets from the solution, cooling the soda cellulose so prepared to a temperature at which mercerization is effected, and xanthating the cooled, mercerized product.

9. A process which comprises dipping sheets of cellulose pulp in a bath of caustic soda solution at a temperature sufficiently high to be nonmercerizing, removing the substantially unmercerized sheets from the solution, and cooling the soda cellulose so prepared to a temperature at which mercerization is effected.

10. In the manufacture of cellulose xanthate, those steps which comprise dipping sheets of wood pulp in a bath of caustic soda solution of about 18% strength at a temperature sufficiently high to be non-mercerizing, removing the substantially unmercerized sheets from the solution, cooling the soda cellulose so prepared to a temperature at which mercerization is effected, and xanthating the cooled, mercerized product.

GEORGE A. RICHTER. 

